Today's internal combustion engines must operate with minimum noise, in addition to low fuel consumption and low emission values.
Mainly in internal combustion engines working by the diesel process, noise emissions should be paid particular attention to. In diesel engines, partially homogeneous and homogeneous combustion processes are used in partial areas of the engine's characteristics map in addition to the conventional, non-homogeneous combustion process in order to achieve minimum emission levels, in particular for nitrogen oxides and soot particles, in these partial areas of the operating characteristics map.
However, due to the high ignition delay, homogeneous and partially homogeneous combustions exhibit intolerable noise emissions, which cannot be fully avoided using measures such as an increased exhaust gas recirculation rate or retarded combustion. Mainly, the transition from a conventional non-homogeneous combustion process to a partially homogeneous or homogeneous combustion process and dynamic changes in the operating state may result in critical noise emissions. To be able to avoid or at least reduce these noise emissions using suitable injection strategies, the noise emissions must be ascertained during the operation of the internal combustion engine.
In a conventional method for detecting the combustion noise, the pressure in the combustion chamber is detected, weighted using a transmission function of the engine block and of the human hearing, and the emitted sound power is computed therefrom. These calculations are very computation-intensive and therefore cannot be implemented in the engine control units normally used today. In addition, internal combustion engines must be equipped with pressure sensors in the combustion chambers for carrying out this method.